The present invention relates to a material for an aperture grille for use in a color picture tube, a producing method therefor, an aperture grille, and a color picture tube incorporating the aperture grille. More particularly, it relates to a material for an aperture grille for use in a color picture tube which has an excellent tensile strength and high temperature creep strength and besides good magnetic characteristics, and relates to a producing method therefor, an aperture grille made thereof, and a color picture tube incorporating this aperture grille.
When an aperture grille is incorporated into a color picture tube, it is welded to the frame of the color picture tube while being applied under great tension. Therefore, a material for making an aperture grille for a color picture tube is required to have a tensile strength of at least 60 kgf/mm2. Accordingly, the materials currently used for the aperture grille of the color picture tube comprise low carbon steel sheets, which have been reinforced by strengthening-forming.
Further, after being welded to the frame of the color picture tube, the aperture grille is subjected to a heat treatment for blackening. This heat treatment is carried out at 455xc2x0 C. which is below the recrystallization temperature of steel for only a short time of about 15 minutes so that after blackening the tapes constituting the aperture grille may not be loosened but can be maintained with its loaded tensile strength. However, under such heat treatment conditions for blackening, the tapes cannot be entirely free from a recovery phenomenon but involve elongation of it by the recovery, thereby suffering cuts and twists. For this reason, a material for an aperture grille for use in a color picture tube is required to have a tensile strength of not less than 60 kgf/mm2 and a creep strength enough to cause no elongation even when subjected to such a heat treatment for blackening as conducted at a temperature of 455xc2x0 C. for a time of 15 minutes and to control its elongation of not more than 0.4% when the aperture grille is applied with a tensile strength of 30 kgf/mm2.
The color picture tube comprises an electron gun and a luminescent screen which converts an electron beam into picture images. The inside of the picture tube is covered with a magnetic shield member so as to prevent the electron beam from being biased by geomagnetism. The aperture grille is also required to be used as the magnetic shield member and, therefore, should be made of a material having a great magnetic flux density (Br) and a small coercive force (Hc) representing the magnetic characteristics, in other words, a material having a great ratio of magnetic flux density to coercive force (Br/Hc). However, such a low carbon steel sheet as mentioned above, which has been subjected to strengthening-forming for obtaining a high tensile strength and also subjected to heat treatment for blackening at a temperature below its recrystallization temperature, has a small magnetic flue density of up to 8 kG and a great coercive force of about 5 Oe. Therefore, it is preferable in the present invention to use a material having a ratio of Br (kG) to Hc(Oe) exceeding 1.7.
So far, methods for improving tensile yield strength of a low carbon steel sheet include a solid solution strengthening method by means of carbon and nitrogen. The more the carbon or the nitrogen increases in the steel, the more increases carbide or nitride so that the movement of ferromagnetic domain walls will be prevented, inducing the impairment of the magnetic characteristics of the steel. Besides, methods for improving creep strength of a low carbon steel sheet include that of precipitating carbide or others in the steel. These precipitates have mostly a large grain size in micron order, which prevent the movement of ferromagnetic domain walls, greatly impairing the magnetic characteristics of the steel. Therefore, this method has not been applied as a method of producing a material for an aperture grille for use in a color cl picture tube.
The present invention has an object to provide a material for an aperture grille for use in a color picture tube which has an excellent tensile strength and high temperature creep strength and superior magnetic characteristics to prior materials, and provide a producing method therefor, an aperture grille made thereof, and a color picture tube incorporating this aperture grille.
The present invention relates to a material for an aperture grille for use in a color picture tube made of a low carbon steel sheet containing 9 to 30 wt % of Ni, and another embodiment of the invention relates to a material for an aperture grille for use in a color picture tube made of a low carbon containing 9 to 30 wt % of Ni and 0.1 to 5 wt % of Co.
Another embodiment of the present invention relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of cold-rolling a low carbon steel sheet containing 9 to 30 wt % of Ni and annealing same at a temperature of 400 to 500xc2x0 C.
Another embodiment of the invention relates to a method of producing a material for an aperture grille for use in a color picture tube comprising the steps of cold-rolling a low carbon steel sheet containing 9 to 30 wt % of Ni and 0.1 to 5 wt % of Co and annealing same at a temperature of 400 to 500xc2x0 C.
Still another embodiment of the invention relates to a method of producing a material for an aperture grille for use in a color picture tube which comprises the steps of cold-rolling a low carbon steel sheet containing 9 to 30 wt % of Ni, subjecting the same to process-annealing at a temperature of 500 to 800xc2x0 C. and another cold-rolling, and annealing same at a temperature of 400 to 500xc2x0 C.
Another embodiment of the invention relates to a method of producing a material for an aperture grille for use in a color picture tube which comprises the steps of cold-rolling a low carbon steel sheet containing 9 to 30 wt % of Ni and 0.1 to 5 wt % of Co, subjecting same to process-annealing at a temperature of 500 to 800xc2x0 C. and another cold-rolling, and annealing same at a temperature of 400 to 500xc2x0 C.
And embodiment of the invention relates to an aperture grille for use in a color picture tube, which is made of a low carbon steel sheet containing 9 to 30 wt % of Ni and another embodiment of the invention relates to an aperture grille for use in a color picture tube, which is made of a low carbon steel sheet containing 9 to 30 wt % of Ni and 0.1 to 5 wt % of Co.
An embodiment of the invention relates to a color picture tube incorporating an aperture grille made of a low carbon steel sheet containing 9 to 30 wt % of Ni and another embodiment of the invention relates to a color picture tube incorporating an aperture grille made of a low carbon steel sheet containing 9 to 30.